PROJECT SUMMARY An estimated 37 million people worldwide are infected with human immunodeficiency virus (HIV). Combined antiretroviral therapy (ART) has turned HIV into a chronic infection with significantly longer life expectancy. New health issues have surfaced as HIV patients live longer. Specifically, 50% of HIV-infected (HIV+) individuals exhibit neurocognitive impairment, termed HIV-associated neurocognitive disorders (HAND). A key event leading to HAND is persistent low-level chronic neuroinflammation resulting in neuronal damage and cell death. A major contributor to HIV-induced neuroinflammation is activated monocytes, which are significantly elevated in patients? with HIV-associated dementia. Activated, CD16+ monocytes are infected by HIV in the periphery and migrate across the blood-brain barrier (BBB) to release HIV virions and neurotoxic and proinflammatory factors. Before entering the CNS, resting (CD16?) monocytes transition into the CD16+ through poorly understood mechanisms including elevated interferon alpha (IFN?), a potent antiviral cytokine produced by plasmacytoid dendritic cells (pDC), an observation consistent with the IFN? gene signature in monocytes from HIV patients. Chronic IFN? production in HIV patients has been linked to neurocognitive impairment. In parallel, IFN? also activates CD8+ T cells, which are recruited from systemic circulation to cross the BBB. Once in the perivascular space, activated monocytes and CD8+ T cells interact with astrocytes to drive a chronic neuroinflammatory response leading to destruction of neurons and declining cognative function. Interestingly, cannabis, which has constituents (e.g., ?9-tetrahydrocannabinol (THC)) possessing immune suppressive and anti-inflammatory activity, is widely used (approximately 25-37%) by HIV patients. The beneficial vs. deleterious effects of cannabinoid therapy in HIV patients remains unknown and understudied. Preliminary results show that THC suppresses IFN?-mediated CD16? to CD16+ monocyte transition as well as IL-7 receptor upregulation on CD8+ T cells. Moreover, HIV+ marijuana-users (MJ+) have fewer circulating CD16+ monocytes compared to HIV+MJ-. Preliminary data is also presented using a novel all human coculture system demonstrating that both monocytes and CD8+ T cells, when cocultured with astrocytes significant drive the secretion of astrocyte-derived inflammatory mediators, including IL-6 and IP-10, a response suppressed by THC. Mechanistic studies are proposed to test the hypothesis: Cannabinoids suppress interferon-?-mediated monocyte and CD8+ T cell activation in the periphery and their detrimental effects on astrocyte function, all of which are key processes in HIV-associated chronic neuroinflammation.